This invention relates to input/output apparatus for a digital computer system, and more particularly to interfaces in such a system for coupling peripheral units for communication with the central processor thereof.
The instant invention is an improvement in an interface defined as an "integrated" interface and described in the U.S. Patent Application for COMPUTER INPUT/OUTPUT CONTROL APPARATUS by A. Bardotti and R. Pederzini, Ser. No. 576,523, filed on Apr. 12, 1975, and assigned to the assignee of the present application.
In the design of modern computer systems, the capability for diagnosis and the protection of information have assumed primary roles. In such design, the capability is provided for the system itself to be able to detect and locate with substantial precision the sources of errors, and to be able to determine, to as great an extent as possible, a remedy for such sources, in order to reduce to a minimum the need for external human intervention. However, such capability provides that the system be able to distinguish between the various possible errors which do not adversely affect the execution of subsequent operations and those errors which may cause erroneous or faulty operation in the execution of subsequent tasks or may cause the damaging or irreparable loss of information.
Such modern computer systems include a central processor coupled to a plurality of peripheral units by channels. Each channel comprises a set of lines on which electrical signals representing information are transferred according to appropriate processes. The physical set of such lines and the group of logical, or control, signals transferred thereon is commonly termed an "interface."
In these modern computer systems, the central processor, in addition to having the capability of detecting errors internal thereto, is often employed for executing diagnostic procedures which enable the identification of faults and errors internal to the peripheral units. To properly execute such procedures, it is essential that the interface be operating properly. However, the interface itself is a possible source of errors in the exchange of information between the central processor and the peripheral units, which errors may be due to two basic causes: electrical disturbances or electrical faults.
Independent from the source itself which generates an error, an error may have two effects. Firstly, if the error occurs during the transfer of control information, the execution of the subsequent operations will be irreparably impaired or faulty; consequently, such an error requires the interruption of the operations in process and the initiation of appropriate diagnostic or alerting procedures. Secondly, if the error occurs during the transfer of data, the error impairs only the transferred data and does not, in general, adversely affect the subsequent operations; consequently, such an error allows subsequent operations to be completed if no errors occur during the following transfer of control information.
Accordingly, it is a principal object of the present invention to provide an improved interface for a computer system.
Another object of the present invention is to provide an interface for a computer system which provides signals for and distinguishes between errors occurring in the system.
Another object of the instant invention is to provide an interface for a computer system which determines whether errors detected in the system are attributable to the interface or to an error internal to the central processor or the peripheral units.
Another object of the present invention is to provide an interface for a computer system which distinguishes between errors occurring during a data transfer or during a conrol information transfer.
Another object of the present invention is to provide a computer system in which an interface distinguishes between errors arising in the system and, according to the source of such errors, enables the performance of the most appropriate procedures for diagnosing or recovering from such errors.